Introduction
USB On-The-Go (OTG) allows two USB devices to talk to each other without requiring the services of a personal computer (PC). Although OTG appears to add peer-to-peer connections to the USB world, it does not. Instead, USB OTG retains the standard USB host/peripheral model, in which a single host talks to USB peripherals. OTG does introduce, however, the dual-role device, or simply stated, a device capable of functioning as either host or peripheral. Part of the magic of OTG is that a host and peripheral can exchange roles if necessary.
Before OTG, the concept of an embedded host was already established in the USB world. Instead of duplicating the full UHCI/OHCI USB controllers and drivers built into PCs, most embedded host chips provide limited hosting capabilities. This makes them better suited to the embedded environment than a PC with its huge resources and infinite capacity for drivers and application software.
An OTG device may, or may not be capable of functioning as a host. It is likely, nonetheless, that most OTG devices will be dual-role.
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